In the hair domain, it is possible to distinguish two types of dyeing.
The first is semipermanent or temporary dyeing, or direct dyeing, which involves dyes capable of giving the natural coloration of the hair a more or less marked color modification which is possibly resistant to several shampooings. These dyes are called direct dyes.
The second is permanent dyeing or oxidation dyeing. The latter is carried out with so-called “oxidation” dyes comprising oxidation dye precursors and couplers. The oxidation dye precursors, commonly called “oxidation bases”, are compounds which are initially colorless or faintly colored which develop their dyeing power inside the hair in the presence of oxidizing agents added at the time of use, leading to the formation of colored and dyeing compounds. The formation of these colored and dyeing compounds results either from an oxidative condensation of the “oxidation bases” with themselves, or from an oxidative condensation of the “oxidation bases” with color modifying compounds commonly called “couplers” and generally present in the dyeing compositions used in oxidation dyeing.
The variety of molecules used, which consist, on the one hand, of the oxidation bases and, on the other hand, of the couplers, makes it possible to obtain a very rich palette of colors.
To further vary the shades obtained with said oxidation dyes, or to increase their glint, direct dyes are sometimes added to them.
The so-called “permanent” dyeing obtained using these oxidation dyes should moreover satisfy a number of requirements. Thus it should make it possible to obtain shades in the desired intensity and should exhibit good resistance to external agents (light, adverse weather conditions, washing, permanent waving, perspiration, rubbing).
The dyes should also make it possible to cover gray hair, and should finally be the least selective possible, that is to say they should make it possible to obtain the smallest possible differences in coloration all along the same keratinous fiber, which may indeed be differently sensitized (i.e. damaged) between its tip and its root.
Compositions which contain these oxidation dyes and which are mixed before use with an oxidizing agent are often provided in the form of water-based creams conventionally comprising fatty alcohols, oxyalkylenated fatty alcohols, and sometimes soaps.
To confine the oxidation dyeing product upon application to the hair so that it does not run over the face or outside the areas which it is desired to dye, associative polymers of the anionic, nonionic or cationic type, and preferably of the nonionic type, have recently been introduced into these compositions.
However, creams based on associative polymers contain a lot more water than conventional creams. With this aqueous medium more rich in water than in the prior art formulations, premature oxidation of the oxidation dyes may occur before their application to the fibers and this may result in colors with shades which are less intense than those expected.